Ringed by barbed wire, the decrepit factory on New Street was fallow for decades, an emblem of the untapped potential of East Boston’s waterfront.

For years, real estate companies proposed transforming the four-acre site, only to delay because of financial difficulties or broader concerns about taking the redevelopment lead in a rundown corner of the city.

Boston police will no longer hold immigrants for possible deportation, unless a criminal warrant has been issued for the person’s arrest, under an ordinance unanimously passed by the City Council on Wednesday.

BOSTON — The Boston City Council approved an ordinance Wednesday that will withdraw the city from a controversial federal immigration program and block Boston Police from detaining immigrants living in the country illegally for deportation in all but extreme circumstances.

The Trust Act, which was unanimously approved by the 13 member council, blocks police from holding immigrants living in the country illegally through the federal program known as Secure Communities unless Immigration and Customs Enforcement officials have a warrant for their deportation.